package WrittenExamination;

import java.util.Scanner;

public class day6 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int h = sc.nextInt();
        int w = sc.nextInt();
        int ecount = (w/4)*2+(w%4 < 2 ?w%4:2);
        int ocount = ((w-2)/4)*2 + ((w-2)%4<2?(w-2)%4:2);
        int ret = h/4*(ecount + ocount)*2;
        if(h%4>0) ret += ecount;
        if(h%4>1) ret += ecount;
        if(h%4>2) ret += ocount;
        System.out.println(ret);
    }
}
